Mild Cognitive Impairment

Mild Cognitive Impairment (MCI) represents a transitional phase between normal aging and dementia, primarily affecting memory. It affects nearly one-fifth of adults over 50 worldwide, highlighting its growing clinical importance. Pharmacological treatments have shown limited efficacy, prompting interest in non-invasive interventions such as transcranial direct current stimulation (tDCS), which modulates cortical excitability through weak electrical currents. This systematic review aimed to evaluate the effects of tDCS on memory performance in older adults with MCI and to identify protocol-specific predictors of improvement. A systematic search was conducted in PubMed, Scopus, and Web of Science (up to April 2025) following PRISMA guidelines. Eligible studies included randomized and non-randomized trials examining tDCS alone or combined with cognitive training in adults aged 60 years and older with MCI. Ten studies (N = 428) met inclusion criteria. Due to heterogeneity, findings were synthesized narratively. Overall, tDCS significantly improved verbal and recognition memory, as well as spatial and episodic memory performance. Neurophysiological findings indicated enhanced neural activity and connectivity. Stimulation targeting the left dorsolateral prefrontal cortex produced the most consistent benefits, especially when applied for ten or more sessions at an intensity of 2 mA. Mild side effects, such as redness and tingling, occurred in approximately 20–30% of participants, with no serious adverse events reported. Preliminary evidence supports the effectiveness and safety of tDCS in improving memory among individuals with MCI. However, variability in protocols and small sample sizes underscore the need for standardized, biomarker-guided, and longitudinal research.